An interlock is a feature that makes the state of two mechanisms or functions mutually dependent. It may be used to prevent undesired states in a finite-state machine, and may consist of any electrical, electronic, or mechanical devices or systems. In most applications, an interlock is used to help prevent a machine from harming its operator or damaging itself by preventing one element from changing state due to the state of another element, and vice versa.
One particular area in which interlock systems are used is in the area of power supplies. When multiple uninterrupted power supplies (UPSs) are connected in series, it is necessary to bypass one of the UPSs before it is taken off-line in order that power is not cut off to the entire system. In order to bypass a UPS in such a power system, it is necessary to flip a number of switches in a particular order to prevent a break in the power line.
The current industry-standard in interlock systems is to provide trapped key interlocks forcing the user to use the key and follow a particular sequence to bypass a UPS. Trapped key interlocking is a method of ensuring safety in industrial environments by forcing the operator through a predetermined sequence using a defined selection of keys, locks and switches.
It is called “Trapped Key” because it works by releasing and trapping keys in a predetermined sequence. After the UPS has been isolated, a key is released that can be used to grant access to a switch that will isolate the UPS from the power system. This allows maintenance or replacement of a given UPS.
However, this is a cumbersome process that involves using and turning keys, which must be placed in the proper order and turned in the proper order before necessary switches can be flipped. It is also a system that leaves open the possibility of error if the sequence is not followed and the keys are turned in the wrong order.
It would therefore be desirable to provide a less cumbersome and more secure way of providing an interlock system.